Recently, many countries including developed countries have been trying to control environmental pollution by strengthening various environmental regulations. In the vehicle industry, researches for improving fuel efficiency have been conducted through weight reduction and the like to satisfy such increasing environmental regulations. Accordingly, weight reduction and high torque requirements for vehicles have been increasingly strengthened.
In order to meet such requirements, researches into weight reduction through use of an aluminum alloy having about ⅓ the density of a conventional steel material have been conducted, and, for example, hypereutectic Al—Si based alloys and the like have been developed.
Hypereutectic Al—Si based alloys also can have superior wear resistance, satisfactory corrosion resistance and a low coefficient of thermal expansion, compared to other Al-based alloys, and thus have been widely used in wear-resistant parts such as a cylinder block or a cylinder block in an internal combustion engine of vehicles.
In general, a hypereutectic Al—Si based alloy includes 16 to 18% by weight of silicon (Si), 0.5% by weight or less of iron (Fe), 4 to 5% by weight of copper (Cu), 0.1% by weight or less of manganese (Mn), 0.45 to 0.65% by weight of magnesium (Mg), 0.1% by weight or less of zinc (Zn), 0.2% by weight of titanium (Ti) and a remainder of aluminum (Al). For instance, in order to secure wear resistance, a certain hypereutectic Al—Si based alloy includes a larger amount of silicon (Si) than that of ADC12-based aluminum alloys. In the related art, an alloy composed of the composition may be referred to as an A390-based aluminum alloy.
As an alloy similar to the A390-based aluminum alloy, an ADC12-based aluminum alloy also has been developed. The ADC12-based aluminum alloy is different from the A390-based aluminum alloy in its compositions, such that the ADC12-based aluminum alloy only includes 9.6 to 12.0% by weight of silicon (Si) unlike the A390-based aluminum alloy. Due to such difference in silicon contents, the ADC120-based aluminum alloy has an elastic modulus of about 71 GPa, however, it may not be suitable for use in vehicle components.
In order to address such problem, technology to enhance elastic modulus and wear resistance of the ADC12-based aluminum alloy using precipitation hardening effects of Al3Ti formed by adding titanium (Ti) and boron (B) to the ADC12-based aluminum alloy has been developed.
For example, ADC12-5Ti-1B may be formed by adding 5% by weight of titanium (Ti) and 1% by weight of boron (B) to the ADC12-based aluminum alloy and has an elastic modulus of about 89 GPa which is an increase of about 25%, as being compared to when titanium (Ti) and boron (B) are not added.
However, a maximum silicon (Si) content of the ADC12-based aluminum alloy is 12% by weight and thus enhancement in properties by increasing the content of silicon (Si) is limited. Accordingly, an A390-5Ti-1B alloy was prepared by adding 5% by weight of titanium (Ti) and 1% by weight of boron (B), as in the ADC12-based aluminum alloy, to the A390-based aluminum alloy having a higher silicon (Si) content than the ADC12-based aluminum alloy. For instance, the A390-5Ti-1B alloy has an elastic modulus of about 90 GPa.
However, a primary Si phase in the A390-5Ti-1B alloy is introduced to Al3Ti that is formed through addition of titanium (Ti) and boron (B) and thus a TiAlSi ternary phase is formed, thereby decreasing elasticity effects, etc. of an aluminum alloy.
Accordingly, the present inventors have tried to develop a hypereutectic Al—Si based alloy which may enhance properties such as wear resistance and the like, by adding titanium (Ti), boron (B), nickel (Ni), and the like in an aluminum alloy.